Holy Paladin 2pT10 bonus and some mouse over nonsense.

While your divine illumination talent is active, your healing spells are 35% faster.

That's 35% more heals at 50% the mana for 15secs every 3mins making Divine Illumination (DI) a very valuable 1-point talent.  So why not maximize the uptime with a simple macro:

#showtooltip Holy Light
/cast Divine Illumination
/cast Holy Light

DI does not cause a GCD, so there will not be a delay on the Holy Light.  This macro can be used as the main heal Nuke.  A version that allows mouse over targeting is here:

#showtooltip Holy Light
/cast Divine Illumination
/cast [target=mouseover] Holy Light; Holy Light

Just move the mouse over your raids unit frames and bomb the raid with Big Heals.

I actually have another line in my macro to clear the spell not ready error that pops up while DI is on CD.  I also have error speech turned off, so it doesn't say anything to me about it.

#showtooltip Holy Light
/cast Divine Illumination
/cast [target=mouseover] Holy Light; Holy Light
/run UIErrorsFrame:Clear() 

I actually have three Holy Light macros on my action bar.  The first is just a basic mouse over Holy Light.  The second the DI version above, the third does a DI and Avenging Wrath.  This allows me to increase my heals more selectively by just shifting to a different heal button.  This level of control is only necessary on the hardest fights.  For the most part the above macro is great when the plan is to just bomb away with Holy Light.